1. Field of the Invention
The present invention relates to capacitors comprising an inert porous shaped body onto which a first electrically conductive layer, a second layer of barium titanate and a further electrically conductive layer have been applied.
2. Description of the Background
Capacitors perform many tasks in information technology and electric energy engineering. There has in recent times been a search for capacitors which have a high energy density and can perform the task of batteries or be used for covering short-term high load requirements.
Electrochemica Acta 45 (2000), 2483 to 2498, discloses electrochemical or double-layer capacitors. These devices, also known as supercapacitors or ultracapacitors, store electric energy in two capacitors which are connected in series and each have an electric double layer which is formed between the two electrodes and the ions in the electrolyte. The distance in which charge separation occurs is only a few Angstrom. As electrolytes, use is made of highly porous carbon having internal surface areas of up to 2 500 m2/g. As indicated by the capacitor formulaC=E0·E·A/dwhere C is the capacitance, E0 is the absolute dielectric constant, E is the dielectric constant of the dielectric, A is the area of the capacitor and d is the distance between the electrodes, capacitances of up to 100 farad/cm3 are possible at large areas A and small spacings d.
Such double-layer capacitors (supercapacitors) at present achieve energy densities of from 3 to 7 Wh/kg or Wh/liter, which are far below the energy densities of conventional batteries (lithium ion batteries achieve from 150 to 200 Wh/kg). This is due to the maximum possible voltage loading being restricted to about 3.5 V by the electrochemical stability of the electrolyte.
On the other hand, there is a type of capacitor which operates at high voltages, namely ceramic capacitors comprising dielectrics based on barium titanate.
Ceramic capacitors which comprise dielectrics based on barium titanate and operate at high working voltages because of the high dielectric breakdown resistance of the titanates of up to 200 V/0.1 μm are known from the prior art. However, ceramic capacitors have relatively low capacitances.
It is an object of the present invention to remedy the abovementioned disadvantages.